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Old 21st December 2012, 03:08 PM   #1
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Default Rotel RA-930BX

Hi all,

I have a problem with my Rotel RA-930BX. It simply is totally off!

Fuses are ok, I measured the AC in the board and it is ok also.

Maybe it's an easy thing, but I can't find where's the problem!

Just stopped listening to the music!

Any help will be much appreciated.
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Old 21st December 2012, 03:36 PM   #2
jaycee is offline jaycee  United Kingdom
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Next step is check the DC supplies at the capacitors. Are they correct?

Is your power light on?
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Old 21st December 2012, 03:42 PM   #3
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No, the power light is off...

The DC supplies at the main caps should have less than 50V but I don't know exactly how much since I don't have a schematics.

I'll measure it.
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Old 21st December 2012, 05:11 PM   #4
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units like that fail once in a million years
If you need a free schematic please email me

things to look at
---Check mains fuse ( Caution required at all mains operated devices )
--- depress tape monitor switch
--- make sure that pots and switches are clean and not scratchy
---selector switch is open onatop and doesn't like dirt
---Tape monitor switch is sealed though might get oxidized or dirty
---Verify all voltage according to the schematic
---Verify connections remember that you have direct speakers and switched speakers
---Verify proper speaker switch pressed

do this and let us know

Kind regards
sakis
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Old 21st December 2012, 05:34 PM   #5
jaycee is offline jaycee  United Kingdom
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Schematic for the RA-930AX can be downloaded from: B&W Group North America Service & Support - Service Manuals

There is very little (if any!) difference between the AX and BX that I can tell.
You should have around +/- 38V supplies at the capacitors. The power LED is powered by the +38V supply, so if that is not lit, you are missing 38V.

I have seen instances where the bridge rectifier has failed in these amps. They are only 4A rated units and that is a bit tight. Replace with at least an 8A one if it has been damaged.
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Old 21st December 2012, 07:34 PM   #6
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Quote:
Originally Posted by jaycee View Post
Schematic for the RA-930AX can be downloaded from: B&W Group North America Service & Support - Service Manuals

There is very little (if any!) difference between the AX and BX that I can tell.
You should have around +/- 38V supplies at the capacitors. The power LED is powered by the +38V supply, so if that is not lit, you are missing 38V.

I have seen instances where the bridge rectifier has failed in these amps. They are only 4A rated units and that is a bit tight. Replace with at least an 8A one if it has been damaged.
Fantastic. The unit is missing +38V. No voltage at the power capacitors.

And for the rectifier, I put my MM at the "beep" sound position and it sounds at all the 4 pins. It should block current at least in one phase, right?
If so, I'll get tomorrow same an 8A rated rectifier...

Last edited by Karl vd Berg; 21st December 2012 at 07:41 PM.
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Old 21st December 2012, 07:39 PM   #7
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Quote:
Originally Posted by sakis View Post
units like that fail once in a million years
If you need a free schematic please email me

do this and let us know

Kind regards
sakis
Thanks! I like this unit. It has plenty of Black Gates inside!
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Old 21st December 2012, 07:59 PM   #8
jaycee is offline jaycee  United Kingdom
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You will need to take the rectifier out to test it, as it would be shunted by the windings on the transformer. I'd say its quite likely that it's toast though.

I'm not sure if those Black Gate's are stock - to me, it looks as if the unit has had all of the capacitors replaced. Still, thats a bonus for you My 930AX is a good sounding amp, and my only complaints with it are the stupid plastic base that has shattered.
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Old 21st December 2012, 08:31 PM   #9
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Quote:
Originally Posted by jaycee View Post
You will need to take the rectifier out to test it, as it would be shunted by the windings on the transformer. I'd say its quite likely that it's toast though.

I'm not sure if those Black Gate's are stock - to me, it looks as if the unit has had all of the capacitors replaced. Still, thats a bonus for you My 930AX is a good sounding amp, and my only complaints with it are the stupid plastic base that has shattered.
Right, I'll take the rectifier out to test it. I can tell it's not "clean" as the other components... Looks a bit burned, but who knows...

Looking at the other side of the PCB, I see no signs of components replaced. All the soldering points seem to be still "original". Also the capacitors still have that nasty glue surrounding them...

What happened is that Rotel always made a model and, after 2 or 3 years "upgraded" it with other components. The RA-930BX is an 1994 release. Like the RA-04 series, the first seems to be from 2006. Then Rotel released the RA-04 Special Edition in 2008 (with better capacitors and resistors). Now the company just released the "new" RA-10 model. Exactly same specifications and design, but different components.
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Old 22nd December 2012, 09:46 AM   #10
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upgrade remarks correct

rectifier can be confusing from trafo windings but also voltage that is stored inside the caps

Again it seems that Rotel got rectifiers that where overestimated or lower quality than supposed to be ..Generally and many Rotels have a history on bowing rectifiers .

A blown rectifier will also mean a mains fuse gone ....carefully with all those

Kind regards
Sakis
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